It has hitherto been a general practice for the bearing device to have the model number, precision code, special requirement code and manufacturing lot number marked in the product itself or printed in a package thereof. However, the contents that can be born in the bearing device and/or the package thereof are limited to the minimum.
As IC tags which are affixed to various products and which are compact in size and capable of recording a large amount of information therein, various IC tags for use in radio frequency identification (RFID) have hitherto been developed, which utilizes the RFID technology. (See, for example, the Japanese Laid-open Patent Publication No. 2002-298116.)
However, the bearing identification information represented by the numbering conventionally marked in the packages containing bearing devices has a problem in that it tends to be lost or become illegible after the bearing device has been assembled. The markings made in the respective bearing devices contain so small an amount of information marked, that individual identification of those bearing devices may not be possible to achieve.
In view of the foregoing, attempts have been made to affix an RFID-based IC tag capable of accommodating a large amount of information directly to each of the bearing devices. However, since the RFID-based IC tag makes use of microwaves, mounting of the RFID-based IC tag on a bearing device makes it impossible for the RFID-based IC tag to be read out because during the information reading raceway members of the bearing device absorbs the microwaves. In other words, if the IC tag having an antenna was mounted directly on an inner race or an outer race of the bearing device, troubles occur as a result of the microwaves being absorbed in the inner and outer race of the bearing device, which are made of metal other than the antenna, and/or other metallic members such as, for example, a bearing housing when the bearing device is incorporated in a real machine. For this reason, it often occurs that difficulty is encountered in reading the information recorded on the IC tag. Although the IC tag itself is available, which is so designed as to be affixed directly to metallic components, such tag is expensive and bulky.
Also, the bearing devices are varying in size (small or large) and thickness (thin or thick) and have a limited space for accommodating the respective IC tag. Because of this, the IC tags, which are ultra small in size and small in thickness, are desired. As the RFID-based IC tag, the RFID-based IC tag disclosed in the Japanese patent publication referred to above makes use of a spirally coiled antenna as an antenna and, therefore, cannot be designed to have a reduced size in a widthwise direction thereof. Although IC tags, including an antenna, designed to be ultra small in size have been suggested, those IC tags have some performance factors such as, for example, information recording capacity sacrificed in the face of compactization and, therefore, it is quite often experienced that a desired amount of information cannot be recorded.